Tidal volume single-breath washin of SF6 and CH4 in transient microgravity

Abstract

We performed tidal volume single-breath washins (SBW) by using tracers of different diffusivity and varied the time spent in microgravity (muG) before the start of the tests to look for time-dependent effects. SF6 and CH4 phase III slopes decreased by 35 and 26%, respectively, in muG compared with 1 G (P <0.05), and the slope difference between gases disappeared. There was no effect of time in μG, suggesting that neither the hypergravity period preceding μG nor the time spent in μG affected gas mixing at volumes near functional residual capacity. In previous studies using SF6 and He (Lauzon A-M, Prisk GK, Elliott AR, Verbanck S, Paiva M, and West JB. J Appl Physiol 82: 859-865, 1997), the vital capacity SBW showed an increase in slope difference between gases in transient μG, the opposite of the decrease in sustained μG. In contrast, tidal volume SBW showed a decrease in slope difference in both μG conditions. Because it is only the behavior of the more diffusive gas that differed between maneuvers and μG conditions, we speculate that, in the previous vital capacity SBW, the hypergravity period preceding the test in transient μG provoked conformational changes at low lung volumes near the acinar entrance.